Detector modules, applied chiefly in computer tomographs are used, for example, in medical imaging in order to obtain images of the body interior of a patient. A computer tomograph includes, inter alia, a device for generating x-radiation, an x-ray detector and a patient support table with the aid of which the examination object can be moved during the examination along a system axis, the Z-axis, in the examination volume.
The device for generating x-radiation generates an x-ray beam that emanates from an x-ray focus rotating about the examination volume. The x-ray beam expanded in the shape of a fan in a slice plane of the examination volume (X-Y plane) perpendicular to the system axis penetrates a slice of the examination object during examinations, for example a body slice of a patient, and strikes the detector elements, situated opposite the x-ray focus, of the x-ray detector. The angle at which the x-ray beam penetrates the body slice of the patient and, if appropriate, the position of the patient support table vary continuously as a rule as the computer tomograph is recording images.
In third generation computer tomographs, the rotating x-ray focus is generated by an x-ray tube that, just like the x-ray detector, is fastened on a rotary frame that can rotate about the examination volume. The speed of rotation of the rotary frame has been increased more and more in recent years in order to achieve faster scanning speeds while recording images. However, even higher scanning speeds are required for new applications of computed tomography such as, for example, examining the heart or the perfusion of vessels.
For reasons of mechanical stability and safety, a limit has meanwhile been reached in third generation computer tomographs that, because of the masses to be moved and of the high acceleration forces resulting therefrom, no longer permits the speed of rotation of the rotary frame to be raised substantially. For this reason, the number of rows of the x-ray detector used has recently been increased in order to be able to detect a larger volume per rotation of the rotary frame. However, this increases the weight and the costs of the detector.
DE 103 02 565 A1 discloses a further computer tomograph in which two x-ray tubes and two x-ray detectors are used simultaneously. However, even such a design increases the weight of the rotating components, and the overall costs of the computer tomograph.
In the meantime, fifth generation computer tomographs in which both the device for generating x-radiation and the x-ray detector are arranged in a stationary fashion are known in order to avoid rotating components. Use is made with these computer tomographs of a target that at least partially surrounds the examination volume of the computer tomograph in a plane. An x-ray focus moving about the examination volume and from which the x-radiation emanates is generated on this target. These computer tomographs therefore manage completely without a mechanically moving x-ray tube.
The target extends in this case either completely or at least over an angle of more than 180° about the examination volume. In the same way, the x-ray detector surrounds the examination volume either completely or over an angle of at least 180°. Thus, for example, U.S. Pat. Nos. 4,158,142 or 4,352,021 exhibit fifth generation computer tomographs in which the target and the x-ray detector respectively surround the examination volume completely or over an angle of 210°.
In virtually all computer tomographs, use is made as x-ray detectors of detector modules that substantially exhibit a parallel architecture. The incident x-radiation is converted here into electric signals either directly or indirectly via optical radiation for each detector element or each detector channel. The electric signals are integrated and digitized in electronic circuits that are arranged directly on the detector elements. The digital data are subsequently transmitted via a high speed slip ring from the rotating part to the stationary part of the computer tomograph in which the image reconstruction takes place in an image computer. As a result of this parallel architecture, the detector costs rise proportionately with the number of detector channels or detector rows. The costs of a multi-row detector module are therefore substantial in the case of fifth generation computer tomographs.